From d2c2d715e17356acf60920d3269de0e174effc73 Mon Sep 17 00:00:00 2001
From: Keith Smiley <keithbsmiley@gmail.com>
Date: Wed, 4 Dec 2024 19:16:32 +0000
Subject: [PATCH] Fix absolute label use in main attribute of py_test

In rules_python you can specify a file from another package like:

```bzl
main = "//path/to:file.py",
```

This didn't work in rules_py since it was taking the main as a string to
manipulate. This appears closer to me to the upstream logic that was
mirrored, so maybe this was changed for another reason
---
 examples/pytest/BUILD.bazel  | 18 ++++++++++++++++++
 examples/pytest/__init__.py  |  0
 examples/pytest/main_test.py |  1 +
 py/private/py_executable.bzl |  5 ++---
 4 files changed, 21 insertions(+), 3 deletions(-)
 create mode 100644 examples/pytest/__init__.py
 create mode 100644 examples/pytest/main_test.py

diff --git a/examples/pytest/BUILD.bazel b/examples/pytest/BUILD.bazel
index 9256da54..e1cf1060 100644
--- a/examples/pytest/BUILD.bazel
+++ b/examples/pytest/BUILD.bazel
@@ -38,3 +38,21 @@ py_test(
     shard_count = 2,
     deps = ["@pypi_pytest//:pkg"],
 )
+
+py_test(
+    name = "absolute_main_test",
+    srcs = [
+        "__init__.py",
+        "main_test.py",
+    ],
+    main = "//examples/pytest:main_test.py",
+)
+
+py_test(
+    name = "main_with_colon_test",
+    srcs = [
+        "__init__.py",
+        "main_test.py",
+    ],
+    main = ":main_test.py",
+)
diff --git a/examples/pytest/__init__.py b/examples/pytest/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/examples/pytest/main_test.py b/examples/pytest/main_test.py
new file mode 100644
index 00000000..8a113993
--- /dev/null
+++ b/examples/pytest/main_test.py
@@ -0,0 +1 @@
+print("loaded as main!")
diff --git a/py/private/py_executable.bzl b/py/private/py_executable.bzl
index f9e5370a..a0809dae 100644
--- a/py/private/py_executable.bzl
+++ b/py/private/py_executable.bzl
@@ -25,8 +25,7 @@ def _determine_main(ctx):
         Artifact; the main file. If one can't be found, an error is raised.
     """
     if ctx.attr.main:
-        # Deviation from rules_python: allow a leading colon, e.g. `main = ":my_target"`
-        proposed_main = ctx.attr.main.removeprefix(":")
+        proposed_main = ctx.attr.main.label.name
         if not proposed_main.endswith(".py"):
             fail("main {} must end in '.py'".format(proposed_main))
     else:
@@ -87,7 +86,7 @@ determine_main = rule(
     implementation = _determine_main_impl,
     attrs = {
         "target_name": attr.string(mandatory = True, doc = "The name of the py_binary or py_test we are finding a main for"),
-        "main": attr.string(doc = "Hint the user supplied as the main"),
+        "main": attr.label(doc = "Hint the user supplied as the main", allow_single_file = True),
         "srcs": attr.label_list(allow_files = True),
     },
 )